Danya Biton is an agent with Mossad.
For some time she has been with the Israeli intelligence organization and has proven her worth and her deadliness many times over. She will leave that group sometime after we first meet her but she will not lose the dedication to fight bad people on behalf of those unable to defend themselves.
Our initial encounter with her is while following the adventures of , the CEO of an engineering company who has an amazing affinity for being in the wrong place when some nasty individuals attempt to do very unpleasant things. Savage does not go looking for trouble - usually - but it does find him. In the case of Biton, on the other hand, she does seek it out as she is "responsible for eliminating terrorists and other enemies of Israel". She is going by the name of Nadya Wheeler when she and Savage first meet but not too long afterwards she reveals her true identity as they become friends and as they learn they can and should trust each other. She will also tell Savage that her first name of Danya meant 'Judgment of God' and the actions forced on her will go a long way in proving it.
In the meeting, we find that Biton was part of a team of five, "all were fluent in English and had deeply established aliases, including expertly forged birth certificates used to acquire government-issued social security numbers, drivers' licenses, and U.S. passports. They had all lived in the United States since graduating from college and being recruited into the elite Israeli intelligence organization".
This familiarity is why, when she is forced to leave Mossad and go into hiding, she already has years of experience blending in and why she chooses the very large United States to go to ground.
Biton is likely in her late 30s based on her impressive record and the fact that we are told she was a decade older than the other members in that team mentioned before. She is in excellent physical shape and no one would argue that she was a very attractive woman, albeit somewhat aloof since she knows lasting relationships were not likely for someone in her line of work, especially someone that carries inside her regret for the many things her vocation has forced her to do.